1. Field of the Invention
The present invention relate to a magnetic tape cartridge, and particularly to a magnetic tape cartridge comprising a cartridge case and a single reel which is rotatably housed in the cartridge case, wherein the single reel includes a reel hub around which a magnetic tape is wound.
2. Description of the Related Art
Conventionally, as magnetic tape cartridges that are used as storage media for an external storage unit of a computer and the like, there have been known those having a cartridge case which rotatably houses a single reel around which a magnetic tape is wound.
As described, for example, in Japanese Unexamined Patent Publication No. 2000-48526, magnetic tape cartridges of this type generally have a cartridge case in which a single reel is rotatably housed. The single reel comprises a resin reel hub, and upper and lower flanges respectively extending radially outward from the outer peripheries of the upper and lower ends of the reel hub. A magnetic tape is wound around the reel hub, and the lower end of the reel hub is closed by a bottom wall.
FIG. 6A is a bottom view showing a reel of a magnetic tape cartridge described in aforementioned Japanese Unexamined Patent Publication No. 2000-48526, with a reel gear being partially removed. FIG. 7 is an enlarged sectional view of the reel taken along line 7-7 in FIG. 6A. Further, reference numeral 2 indicates a synthetic resin reel, 21 indicates a reel hub, 21a indicates a bottom wall of the reel hub 21, and 22 is a lower flange of the reel 2. A crown gear type reel gear 24 to be meshed with a driving gear of a rotary driving member provided in a drive device (for simplicity purposes, hereinafter referred to as a “drive-side rotary driving member”) is formed in an annular form with the reel hub 21 at an outer peripheral portion of a lower surface of the bottom wall 21a of the reel hub 21. Further, a disk-shaped metal plate 25′ as shown in FIG. 6B is attached to the reel gear 24 by insert molding so as to be positioned concentric with and radially inward of the reel gear 24 for magnetic attraction with respect to the drive-side rotary driving member, thus maintaining the meshed state between the reel gear 24 and the driving gear.
The reel gear 24 of the reel hub 21 is an important part that serves as a reference for measuring the dimensions of the reel and the like. As is apparent from FIG. 7, a portion where the reel gear 24 is formed has a thickness greater than that of the remaining portions, and a so-called “sink mark” is apt to occur during molding. This is one of the causes of narrowing the range of molding conditions.
Further, in the magnetic tape cartridges of this type, as disclosed in, for example, U.S. Pat. No. 6,700,742, a locking member that is movable in an axial direction of the reel 2 between a locked position for blocking rotation of the reel 2 when the magnetic tape cartridge is in a not-operating state and a release position for releasing a locked state of the reel 2; an urging member (coil spring) for urging the locking member in the direction toward the locked position thereof; and a releasing member for moving the locking member in the direction toward the release position thereof in association with meshing between the driving gear of the drive-side rotary driving member and the reel gear 24; are provided within the reel hub 21. The locking member has lock teeth which are brought into mesh with lock teeth provided on the upper surface of the bottom wall 21a of the reel hub 21, and the reel 2 is thereby forcibly locked to block the rotation of the reel when the magnetic tape cartridge is in the non-operating state. In this manner, the tape cartridge is constructed such that the winding of the magnetic tape is not tightened or loosened upon impact due to being dropped or the like.
The aforementioned releasing member (e.g., release pad) has, as disclosed, for example, in U.S. Patent Application Publication No. 20020181152, comprises three legs which respectively protrude outward through three through holes 26 formed in a pawl portion of the reel gear 24, when the driving gear and the reel gear 24 are not meshed with each other. In association with meshing between the reel gear 24 and the driving gear, these legs are pushed back into the through holes 26, and hence the releasing member pushes the locking member up against the urging force of the urging member. As a result, the meshing between the aforementioned lock teeth is released and the reel 2 is thereby allowed to rotate.
In view of the foregoing, an object of the present invention is to broaden the range of hub molding conditions by preventing a “sink mark” from occurring during molding by preventing the thickness of the portion where the reel gear is formed from becoming larger than that of the remaining portions.